Topical steroid formulations containing 21-chloro-9-fluoro-11.beta.-hydroxy-16.alpha.,17-[(1-methylethylidene)bis( oxy)]pregn-4-ene-3,20-dione as the active ingredient are extensively employed in the treatment of skin disorders, such as dermatitis. To be therapeutically effective, the active ingredient must be in a molecular dispersion to facilitate desired percutaneous absorption which is particularly important in achieving a therapeutic response for the management of psoriasis.
The above steroid is insoluble in water (less than 0.0005% soluble) but has been found to have acceptable solubility in certain polyol vehicles, especially polyethylene glycols. However, the steroid is subject to metal catalyzed degradation. Until now, disodium ethylenediaminetetraacetic acid (Na.sub.2 EDTA.2H.sub.2 O) has been employed to inhibit such degradation. However, the Na.sub.2 EDTA.2H.sub.2 O has only low solubility (less than 0.003%) in the polyol vehicle and EDTA and/or the disodium salt tends to precipitate out of the steroid formulation and reduces product stability.